In this study, 3D images of the strain fields in individual nanodiamond crystals were obtained with Bragg coherent diffraction imaging. With this method, the crystal is illuminated with a coherent X-ray beam which scatters to form a coherent diffraction pattern. A series of these diffraction patterns measured from the crystal are used to reconstruct the 3D shape and, more importantly, the strain state of the crystal. One such 3-D image of a nanodiamond is shown here, with the surface coloration indicative of local strain.
Researchers may have developed a cheaper and easier alternative to improving defect-ridden, low-quality, commercially manufactured diamonds by simply heating them up.
A team from Argonne National Laboratory in Illinois and the University of Chicago, have devised a method to heal diamond nanocrystals under high-temperature conditions, while visualizing the crystals in three dimensions using an X-ray imaging technique.
“Quantum sensing is based on the unique properties of certain optically active point defects in semiconductor nanostructures,” F. Joseph Heremans, an Argonne National Laboratory staff scientist and co-author on the paper, said in a statement.
The use of quantum sensing could be a revolutionary in advancing medical diagnostics, enabling new drug development and improving the design of electronic devices.
However, for use in quantum sensing, the bulk nanodiamond crystal surrounding the point defect must be basically perfect and any deviation from perfection—which includes missing atoms, strains in the crystalline lattice of the diamond or the presence of other impurities—will negatively affect the quantum behavior of the material.
These defects, including the nitrogen-vacancy centers in diamonds, are created when a nitrogen atom replaces a carbon atom adjacent to a vacancy in the diamond lattice structure.
They are extremely sensitive to their environment, making them useful probes of local temperatures as well as electric and magnetic fields with a spatial resolution more than 100 times smaller than the thickness of a human hair.
While perfection is needed, highly perfect nanodiamonds are currently both expensive and difficult to make.
Diamonds are biologically inert, meaning quantum sensors based on diamond nanoparticules—which can operate at room temperature and detect several factors simultaneously—could even be placed within living cells where they could, according to Heremans, “image systems from the inside out.”
The science team was able to map the distribution of the crystal strain in nanodiamonds and to track the healing of these imperfections by subjecting them to up to 800 degrees Celsius in an inert helium environment.
“Our idea of the ‘healing’ process is that gaps in the lattice are filled as the atoms move around when the crystal is heated to high temperatures, thereby improving the homogeneity of the crystal lattice,” Stephan Hruszkewycz, also a staff scientist at Argonne and lead author on the paper, said in a statement.
The research team monitored the nanodiamond healing with a 3D microscopy method caked Bragg coherent diffraction imaging, which is performed by subjecting the crystals to a coherent X-ray beam at the Advanced Photon Source at Argonne.
The X-ray beam that scatters off the nanodiamonds was detected and used to reconstruct the 3D shape of the nanocrystal and the strain state of the crystal, according to Hruszkewycz.
The experiments showed that nanodiamonds shrunk during the high-temperature annealing process, which is believed to have occurred because of a phenomenon called graphitization, which occurs when the surface of the material is converted from the normal diamond lattice arrangement into graphite, a single layer of chicken-wire-like arranged carbon atoms.
According to Hruszkewycz, this marks the first time that Bragg coherent diffraction imaging has been shown to be useful at high temperatures, which enables the exploration of structural changes in important nanocrystalline materials at high temperatures that are difficult to access with other microscopy techniques.
Hruszkewycz said the research represents a significant step towards developing scalable methods of processing inexpensive, com
